A growing number of uses and applications for information continue to fuel an interest in increasing the amount of information that can be cost effectively transmitted among sites on an information network. In many situations, optical communication has emerged as a preferred technique for high-speed information transmission. Wavelength division multiplexing (“DWDM”), which involves transmitting multiple colored optical signals over a common communication path, offers the potential to significantly increase the bandwidth or information carrying capability of that communication path. DWDM technology generally increases the information carrying capability of the path in proportion to the number of colored signals that can coexist on that path, wherein each colored signal transmits in a wavelength channel. However, the general complexity and expense of most conventional DWDM technologies, places DWDM communication out of reach of many cost sensitive applications.
Most conventional DWDM systems use single mode laser sources that output highly monochromatic light signals. Those signals typically provide a single concentrated peak of photonic energy at a selected wavelength aligned to the DWDM channel and thereby exhibit high spectral purity. Conventional technologies for controlling such single mode lasers to maintain wavelength alignment with their respective DWDM channels often entails detrimental complications. For example, most conventional DWDM lasers need precise temperature regulation, hermetic packaging, and stray light isolation to operate within DWDM specifications and to maintain wavelength alignment to an assigned DWDM channel. Achieving a sufficient level of such temperature regulation, hermetic packaging, and stray light isolation using conventional technologies can entail manufacturing complexities, operational expenses, excessive power consumption, and bulky size. Such drawbacks often inhibit DWDM communication from applications that could benefit from greater bandwidth.
One conventional approach to providing more than one colored signal on a communication link is coarse wavelength division multiplexing (“CWDM”). Conventional CWDM lasers usually operate without active cooling and output a single mode of light. That single mode of light drifts in wavelength in response to temperature change until reaching a wavelength at which the mode hops. Thus, a conventional CWDM laser may output a single spectral peak of light that responds to temperature change by drifting from a lower end of a wavelength region towards a higher end of that region and then suddenly jumping back to the lower end. The wavelength span of the drifting and mode hopping is often more than 20 nanometers (“nm”), thereby undesirably limiting the number of CWDM channels that can coexist on a particular optical communication link. Further, in many circumstances, such mode hopping can be detrimental to communication integrity and can adversely impact bit error rate.
Another conventional approach to optical communication involves directly modulating free running Fabry Perot lasers. A conventional free running Fabry Perot laser typically generates multiple modes of light that are free to drift within the laser's gain profile. That is, the laser's gain medium has a capability to amplify light across a wavelength span, and the conventional laser's multimode output is generally free to shift and move about within that span. The breadth of that drift and gain profile usually limits the number of conventional Fabry Perot lasers that can concurrently transmit signals over a common communication link and thereby limits the link's accessible bandwidth. For example, some conventional communication networks have at one end of an optical fiber a free running Fabry Perot laser with a gain profile that is nominally centered at 1310 nm and, at the opposite end of the fiber, another free running Fabry Perot laser with a gain profile that is nominally centered at 1550 nm. The 1310 nm laser and the 1550 nm laser transmit signals in opposite directions, and each of those signals can drift within the gain profile of its respective laser.
Conventional technologies for manufacturing optical communication devices are also often undesirably inefficient, costly, or slow. Fabrication often involves expensive processes and systems for forming, processing, aligning, or attaching optical components. Complexity associated with conventional optical device fabrication can limit the extent to which optical networking can address cost sensitive applications.
To address these representative deficiencies in the art, what is needed is a capability for cost effective DWDM communication. The capability should provide optical signals that are robustly aligned to DWDM channels. Another need exists for confining a multimode optical signal to a specified wavelength range. Yet another need exists for cost effective fabrication of optical devices. Such capabilities would support enhancing an optical communication system's bandwidth and would server cost sensitive applications.